For incident energies above the K-shell ionization threshold, around 90 percent of scattering occurs from K-shell electrons [1]}. If both electrons of each scatterer is ejected from the K-shell, it is reported that the dependence of their angular distribution on the relative azimuth \(\eta \)  is proportional to \(\sin ^{2}\eta \) , which is maximum for perpendicular azimuths and zero for coplanar azimuths. Therefore, it is expected that some 65 percent of coincidences will correspond to both electrons originating in the K-shell. One may therefore expect to also observe these azimuthal correlations in Compton scattering experiments [2]}.

